Hi Alex,
Head First Design Patterns is a great book, but it is basically a new explanation of the patterns introduced in the classic Design Patterns text (Addision Wesley 1994). Many other "Patterns" books focusing on different problem spaces have come (and gone) since then, including: Core
J2EE Patterns, SOA Patterns, Wiki Patterns, etc.
If you're interested in learning about what promise Mashups hold as a new development paradigm, then my book is for you